TAXOL DISPOSITION AND METABOLISM

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The objective of this proposal is to develop an improved understanding of the disposition of the antineoplastic drug taxol in humans in studies that will be conducted in parallel with clinical trials of taxol in patients with advanced malignancies. Based on preliminary observations our general working hypothesis is that multiple processes (blood binding, metabolism, biliary excretion) determine the delivery and actions of taxol in man and that interactions with these processes might affect the clinical efficacy and toxicity. This hypothesis will be tested in vivo and in vitro, using cells and subcellular preparations, in three interrelated Aims. In Aim 1 we will establish the disposition of taxol in patients, for the first time using radioactively labeled drug. The pharmacokinetics of taxol, including its blood binding, its metabolism and its excretion by the urinary and fecal routes will thus be determined. Of particular importance is to determine potential dose- dependency in these processes and to establish a complete account of administered taxol dose. We will also characterize an energy-dependent high affinity uptake of taxol by platelets and determine its importance for taxol disposition. In Aim 2 we will address the metabolism of taxol in vitro, using human liver homogenates and microsomes. The qualitative metabolic fate will first be established, using HPLC isolation techniques and tandem mass spectrometry. We will next determine the kinetic aspects of taxol metabolism and the extent and mechanisms of potential drug and other interactions. Identification of the cytochrome P450 isoenzyme(s) involved will be accomplished with isoenzyme-specific antibodies (catalytic activities, Western analysis) and stable cDNA expression systems. Biological activities of taxol metabolites will be determined in vitro. In Aim 3 we will determine the mechanism of and the potential drug interactions with the biliary secretion of taxol and taxol metabolites. This will be done in vivo in the rat as a model of humans as well as in vitro, using bile canalicular membrane vesicles for studies of specific active transport processes. Of particular importance is studies of concentration-dependency and the potential involvement of the multiple drug resistance transporter (P-glycoprotein). Overall, the proposed studies will focus on the three major processes governing taxol disposition, i.e., blood binding, metabolism and biliary secretion, each of which could have profound influence on the efficacy and toxicity of taxol.